The present application is based on and claims priority to Japanese Patent Application Nos. 11-136908, filed May 18, 1999, 11-136909, filed May 18, 1999, and 11-136910, filed May 18, 1999, the entire contents of which are hereby expressly incorporated by reference.
1. Field of the Invention
The present invention generally relates to fuel-injected two-stroke engines for outboard motors. More particularly, the present invention relates to improved control systems for such engines.
2. Related Art
Two cycle engines are widely used, particularly in applications where high specific outputs and relatively uncomplicated, simple engine constructions are desirable. Thus, two cycle engines are frequently employed as power plants in marine outboard motors because of the small space available in the powerheads of such engines and the demand for relatively high performance.
The two cycle engines, however, tend to be very temperamental. For instance, during idle operation, the engines often experience rough operation because of poor scavenging efficiencies. Poor scavenging leaves larger amounts of exhaust gases within the combustion chamber at the end of the exhaust cycle and, therefore, reduces the amount of fresh oxygen available for combustion. Thus, power output may vary from cylinder to cylinder and from stroke to stroke.
In some instances, poor scavenging efficiencies are caused by low air flow rates into the combustion chamber. Accordingly, to increase the displacement of the exhaust gases during the exhaust cycle, the throttle can be opened slightly more. This, of course, results in an increase in power and a higher rate of engine operation during idle, which can cause shifting difficulty with a shiftable transmission.
Moreover, movement of the transmission between drive and neutral results in differing loads being placed on the engine. Accordingly, the engine idle speed varies depending upon the drive state of the transmission. Particularly, the engine typically idles at a lower speed when the transmission is in a neutral drive state, which further compounds the scavenging problem described above. Accordingly, vibrations often develop within the hull of the watercraft due to rough idling with the transmission set in a neutral position.
A further difficulty with two cycle engines relates to so-called over-revving of the engine. Such over-revving can occur, for instance, when the propeller skids as a result of cavitation, or when the engine is raced while in neutral. Often such over-revving is limited by misfiring a cylinder such that the engine speed is reduced. During such misfiring, the fuel injectors typically continue to inject the same amount of fuel as normal operation into the combustion chamber to cool the piston in the misfired cylinder. In addition, the cylinder continues to have exhaust strokes. Accordingly, a fresh charge, which includes less residual exhaust gas, more oxygen and, sometimes, more fuel remains within the combustion chamber of the misfired cylinder. After the over-revving has been corrected, the cylinder then is fired. The return to firing can be accompanied by an abnormally high pressure following combustion. In some circumstances, a gasket between the cylinder head and the cylinder body can be blown through. Of course, this is a potentially serious situation encountered following over-revving of some corrected two cycle engines.
Moreover, during warm-up, direct injected engines often employ an increased idle speed to help warm the engine and to decrease idle speed fluctuations during start-up. However, the warm-up speed often is only maintained for a preset period. In some instances, this preset period of time is insufficient to achieve a high enough operating temperature and the engine cannot maintain operation due to poor fuel atomization. Thus, the engine may have a cylinder that misfires after the idle speed drops. The misfire can cause the engine to stall. Accordingly, this is yet another difficulty with direct injected two cycle engines.
For the above reasons, it is desired to have a two cycle direct injected engine that is controlled to remediate at least one, but preferably more than one, of the aforementioned drawbacks.
Accordingly, one aspect of the present invention involves an outboard motor comprising an engine and a propulsion unit. The engine has an output shaft and the propulsion unit comprises a propeller shaft. A shiftable transmission is interposed between the output shaft and the propulsion unit. The shiftable transmission is adapted to move between a neutral state and a drive state whereby movement of the output shaft is removed from the propeller shaft when the shiftable transmission is in the neutral state and movement of the output shaft is transferred to the propeller shaft when the shiftable transmission is in the drive state. The outboard motor further comprises a control unit adapted to control at least one operating parameter of the engine. A shift detector is in electrical communication with the control unit and is adapted to output a signal indicative of a shift state of the shiftable transmission. An engine speed sensor is in electrical communication with the control unit and is adapted to output a signal indicative of an engine speed. A throttle angle sensor is in electrical communication with the control unit and is adapted to output a signal indicative of a throttle angle. The control outputs a first signal if a first input condition is satisfied and outputs a second signal if a second input condition is satisfied.
Another aspect of the present invention involves a method of controlling a direct injected engine with a controller. The method comprises sensing a shift position, sensing an engine speed and comparing the sensed engine speed to a preset engine speed. A throttle position is sensed and compared to a preset throttle position. A first action is taken depending upon the sensed shift position as long as the sensed engine speed is lower than the preset engine speed and the sensed throttle position is lower than the preset throttle position.
A further aspect of the present invention involves a method of controlling a direct injected engine with a controller. The method comprises an over revolution limiting routine that comprises sensing an engine speed, comparing the sensed engine speed with a first preset speed, taking a first evasive action if the sensed engine speed exceeds the first preset speed, comparing the sensed engine speed with a second preset engine speed and taking a second evasive action if the sensed engine speed exceeds the second preset speed.
Another aspect of the present invention involves a method of controlling a direct injected engine with a controller. The method comprises advancing an ignition timing of the engine a first preset advance amount, sensing an engine speed and starting a counter, comparing the sensed engine speed to a first preset speed and the counter value to a preset value, changing the ignition timing to a second preset advance amount when the sensed engine speed exceeds the first preset speed or the counter value exceeds the preset value.
A further aspect of the present invention involves an engine comprising at least one cylinder with a piston being mounted for reciprocation within the cylinder. A cylinder head is mounted to the cylinder and cooperates with the piston and the cylinder to define a variable volume combustion chamber. A fuel injector is disposed to supply a fuel charge to the combustion chamber and a fuel supply system communicates with the fuel injector. The fuel supply system comprises a high pressure portion and a low pressure portion. The fuel injector is positioned along the high pressure portion with a bypass line connecting the high pressure portion and the low pressure portion. A valve is positioned along the bypass line and a controller is adapted to control the valve such that a flow rate through the bypass line can be controlled.